1. Field of the Invention
The present invention relates to a structure of a filter element of an air cleaner unit of an open element type built in an engine of an automobile and the like.
2. Description of the Related Art
Although a typical air cleaner unit built in an air suction system of an automobile engine is of a covered type in which a filter element is housed in an air cleaner case connected to a suction duct, an air cleaner unit of an open element type, in which a filter element itself is directly connected to a suction duct without any cover such as an air cleaner case, is also known as one of options or replacement parts.
In such an open-element air cleaner unit, since the filter element is exposed outside, the air suction efficiency is higher than that of the covered type, by which an output increase effect of the engine can be obtained. Therefore, the open-element air cleaner unit is often substituted for an existing one in, for example, a sports car. However, since the mount space in an engine room is limited, the shape and structure of the filter element are so designed as to achieve high air suction efficiency.
FIG. 2 is a sectional view showing an example of a conventional air cleaner unit 10 of the above-mentioned open element type. A filter element 11 is shaped like a tapered cylinder with a filter wall made of an adequate filter material, such as paper, cloth and nonwoven cloth, and having a zigzag shaped cross section. A ring-shaped connecting member 12 made of synthetic rubber and having a suction duct connecting opening 12a, and an edge member 13 made of synthetic rubber with a metallic blank cap member 13a, are respectively integrally connected by vulcanization adhesion to ends of major and minor diameter side openings of the filter element 11. The air cleaner unit 10 is mounted in an engine by fixing the suction duct connecting opening 12a in engagement with a joint fitting 20 connected through a joint collar 21 made of rubber and the like, and connecting the collar 21 to an inlet pipe 22 on the side of the engine.
Only a peripheral part of the blank cap member 13a of the air cleaner unit 10 and the edge member 13 may be combined into one rubber ring.
In the conventional air cleaner unit 10 shown in FIG. 2, the filter element 11 is formed as a tapered air suction plane having a zigzag shaped cross section, by which a large air suction area can be secured even if the occupation capacity, that is, the outer dimensions thereof, are relatively small. Accordingly, it is possible to efficiently suck more air with the filter element 11 having small outer dimensions.
However, it is pointed out that turbulent flow arises almost just under the blank cap member 13a when air is sucked through the tapered cylindrical filter wall of the filter element 11 in the above-mentioned conventional air cleaner unit 10, and that the turbulent flow makes the air suction sound louder and causes a considerable loss of sucked air.